John L. Day

Cobalt Plaque Therapy of Posterior Uveal Melanomas

One hundred patients with choroidal melanomas who were treated by the authors with cobalt plaque radiotherapy were analyzed with regard to tumor regression, visual results, complications, and mortality rate. The follow-up period at the time of this writing ranged from one to five years. These preliminary observations indicate that cobalt plaque radiotherapy induces tumor regression in 96% of cases, preserves useful vision in many cases and has fewer complications during the one- to five-year follow-up period than previously believed.

Malignant intraocular tumors

The role of the radiation therapist in the management of malignant intraocular tumors is changing. With more active identification of malignant intraocular tumors, and a better recognization of the manner in which one can deal with problems of radiation sensitivity, radiation techniques of all sorts will be more actively employed in the treatment of these tumors. Special techniques must be selected for appropriate circumstances of management in order to diminish to an absolute minimum the impact upon the lens, the impact upon visual acuity and the impact upon the cornea. Cobalt‐60 plaques are being used more commonly in the treatment of melanomas of the choroid, and the role for radiation therapy in the management of retinoblastoma is changing markably to where it may be used as the primary treatment program rather than enucleation. In metastatic disease involving the uveal tract, radiation therapy has assumed the most important role for management. Chemotherapy should be considered as an active adjuvant in the management of not only those individuals with retinoblastoma but also in those identified circumstances where metastases to the uveal tract are being treated. The role for chemotherapy or immunotherapy in malignant melanoma is unclear.

Regression of posterior uveal malignant melanomas after cobalt plaque radiotherapy

We reviewed the records of 17 patients with posterior uveal malignant melanoma who had been followed for at least 3 months prior to cobalt plaque radiotherapy and whose tumor had been documented to enlarge in thickness during that interval. We evaluated the relationship between the rates of pretreatment tumor enlargement and post-treatment tumor shrinkage using linear regression analysis. We found that the rate of postirradiation tumor shrinkage correlated strongly with the rate of preirradiation tumor enlargement regardless of whether the pretreatment rate of growth was slow, intermediate or rapid. We speculate that the more rapidly regressing tumors were more mitotically active than their more slowly regressing counterparts. If true, the survival rate of patients whose posterior uveal malignant melanomas regress rapidly following radiation therapy may prove to be worse than that of patients whose tumors regress slowly.

A Breast Phantom Method for Evaluating Mammography Technique

A new breast phantom has been designed for use in evaluating mammographic system performance. This phantom incorporates simulated calcifications and fibrillar objects in fat, of graded size, to permit measurements of detail visibility. A special methodology has been developed for measuring visible object size to achieve reproducible and clinically relevant results. Materials and construction of the phantom also permit carrying out dosimetry with an appropriate ionization chamber. Dosage and detail visibility measurements are reported for the Xerox 125, Min-R and Xonics systems. In addition to providing information regarding technique and image receptors, these results demonstrate the usefulness of the basic phantom design, and suggest possible improvements.

Some Physical Measurements of the “Electron Radiography” System

Studies are in progress on imaging characteristics of “electron radiography” (ERG), a new electrostatic system. Wide exposure latitude images have been obtained with patient exposures comparable to those of conventional radiography. This paper reports comparison measurements on an experimental ERG unit and Par Speed screens used with Eastman RP film, density vs. exposure response, edge-imaging characteristics, and image noise.

Choroidal Melanoma: Role of Brachytherapy in Management

The eye is a complex organ made up of the lids, extraocular, and intraocular structures. There is a wide diversity of opinion as to the role for radiation therapy in the management of malignant tumors of the eye. Some authors have stated that all primary intraocular malignant tumors with the exception of retinoblastoma are best treated by surgical techniques (Arnesen and Normes 1975; Ashton and Wybar 1966; del Regiato and Spjut 1977; Jam 1964; Keller 1973; Lederman 1964; Stallard 1966a; Starr and Zimmerman 1962; Winter 1963, 1964). They go on to point out that the only possible reason to irradiate the eye in patients with such lesions would be to preserve vision. Further, it has been stated that irradiation to cancericidal levels may produce an iridocyclitis, resulting in an imbalance between aqueous production and absorption ending in glaucoma. Even given circumstances under which definitive radiation therapy may be pursued, it should be limited to lesions that are located in the posterior half of the eyeball.

Radiation Therapy for Malignant Intraocular Tumors

There is a wide role for radiation therapy in the management of malignant tumors of the eye. Some investigators state that all primary intraocular malignant tumors, with the exception of retinoblastoma, are best treated by surgical techniques. They point out that the reason to irradiate the eye in patients with such lesions would be to preserve vision. These investigators further state that irradiation to cancerocidal levels may produce an iridocyclitis, resulting in an imbalance between aqueous production and absorption ending in glaucoma. In the past, definitive radiation therapy was pursued only if the lesion was located in the posterior half of the globe. However, with the advent of contemporary innovative techniques of radiation therapy, reassessment of this position indicates that there are specific circumstances under which malignant tumors of the eye can be treated successfully.

Storage containers for iridium-192 sources

The advantages of 192Ir for interstitial therapy are well known. Fine wire and spaced seeds in nylon tubing have become available, of which the seeds offer logistic advantages to North American users. These are conveniently obtainable bimonthly in 11 cm active length nylon tubes with 12 seeds 1 cm apart. The best half life figure is 74.4 d, with a gamma constant very close to 5.0 R mCi-1 h-1 at 1 cm. Quoted shielding data varies from 2.4 to 6mm Pb HVT.